[Intel-gfx] [PATCH] drm/i915/execlists: Check preempt-timeout target before submit_ports

[Tvrtko Ursulin]

On 26/04/2020 10:42, Chris Wilson wrote:
> We evaluate *active, which is a pointer into execlists->inflight[]
> during dequeue to decide how long a preempt-timeout we need to apply.
> However, as soon as we do the submit_ports, the HW may send its ACK
> interrupt causing us to promote execlists->pending[] tp
> execlists->inflight[], overwriting the value of *active. We know *active
> is only stable until we submit (as we only submit when there is no
> pending promotion).
> 
> [   16.102328] BUG: KCSAN: data-race in execlists_dequeue+0x1449/0x1600 [i915]
> [   16.102356]
> [   16.102375] race at unknown origin, with read to 0xffff8881e9500488 of 8 bytes by task 429 on cpu 1:
> [   16.102780]  execlists_dequeue+0x1449/0x1600 [i915]
> [   16.103160]  __execlists_submission_tasklet+0x48/0x60 [i915]
> [   16.103540]  execlists_submit_request+0x38e/0x3c0 [i915]
> [   16.103940]  submit_notify+0x8f/0xc0 [i915]
> [   16.104308]  __i915_sw_fence_complete+0x61/0x420 [i915]
> [   16.104683]  i915_sw_fence_complete+0x58/0x80 [i915]
> [   16.105054]  i915_sw_fence_commit+0x16/0x20 [i915]
> [   16.105457]  __i915_request_queue+0x60/0x70 [i915]
> [   16.105843]  i915_gem_do_execbuffer+0x2d6b/0x4230 [i915]
> [   16.106227]  i915_gem_execbuffer2_ioctl+0x2b0/0x580 [i915]
> [   16.106257]  drm_ioctl_kernel+0xe9/0x130
> [   16.106279]  drm_ioctl+0x27d/0x45e
> [   16.106311]  ksys_ioctl+0x89/0xb0
> [   16.106336]  __x64_sys_ioctl+0x42/0x60
> [   16.106370]  do_syscall_64+0x6e/0x2c0
> [   16.106397]  entry_SYSCALL_64_after_hwframe+0x44/0xa9
> 
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> Cc: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> ---
>   drivers/gpu/drm/i915/gt/intel_lrc.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/i915/gt/intel_lrc.c b/drivers/gpu/drm/i915/gt/intel_lrc.c
> index c8014c265ffb..cbd04b74ae2a 100644
> --- a/drivers/gpu/drm/i915/gt/intel_lrc.c
> +++ b/drivers/gpu/drm/i915/gt/intel_lrc.c
> @@ -2438,8 +2438,8 @@ static void execlists_dequeue(struct intel_engine_cs *engine)
>   		clear_ports(port + 1, last_port - port);
>   
>   		WRITE_ONCE(execlists->yield, -1);
> -		execlists_submit_ports(engine);
>   		set_preempt_timeout(engine, *active);
> +		execlists_submit_ports(engine);
>   	} else {
>   skip_submit:
>   		ring_set_paused(engine, 0);
> 

Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin at intel.com>

Regards,

Tvrtko